(1) Field of the Invention
The present invention relates to a planar wave guide type optical amplifier for amplifying a light signal passing through an optical fiber, a method of manufacturing the planar wave guide type optical amplifier, and a laser oscillator using the planar wave guide type optical amplifier, and more specifically, to a planar wave guide type optical amplifier to which a rare earth element is doped and a method of manufacturing the same and a device using the same.
(2) Description of the Related Art
In general, a fiber type light amplifier including an optical fiber having a core doped with a rare earth element such as erbium (Er) or the like is used as a light amplifier used in an optical communication system.
FIG. 1 is a diagram showing the arrangement of a fiber type light amplifier, A signal light with a wave-length of 1.53 .mu.m passing through an optical fiber 31 is input to a wave synthesizer 32. The wave synthesizer 32 synthesizes a pumping light with a wavelength of 1.48 .mu.m supplied from a pumping light output unit 33 and the signal light and supplies the same to an Er-doped optical fiber 34. The Er-doped optical fiber 34 absorbs the pumping light and amplifies the signal light. A wave separator 35 separates the amplified signal light from the pumping light which has not been absorbed by the Er-doped light fiber 34 and outputs only the signal light to an optical fiber 36.
Nevertheless, this fiber type light amplifier has a drawback in that the attachment of the wave synthesizer 32 and wave separator 35 to the Er-doped optical fiber 34 and the adjustment thereof is time consuming. Further, the miniaturization of the amplifier as a whole is difficult because a lower limit exists in the winding radius of the long Er-doped optical fiber 34 and an extra length is needed to the portion of the Er doped optical fiber 34 to be connected to the wave synthesizer 32 and wave separator 35.
To overcome the above drawback, there is recently proposed a planar wave guide type optical amplifier including an amplifying core, a core having a function as a wave synthesizer, and a core having a function as a wave separator formed thereto, these cores being made by etching a glass film obtained by doping a rare earth element such as erbium (Er) or the like on a silicon substrate or quartz glass substrate.
Nevertheless, this planar wave guide type optical amplifier has a problem in that since the cores are entirely doped with the rare earth element when manufactured, a signal light and a pumping light are damped by the cores other than the amplifying core so that an amplifying ratio of the planar wave guide type optical amplifier as whole cannot be increased, Further, even if the cores other than the amplifying core are not doped with the rare earth element, the signal light and the pumping light are damped by the rare earth element doped to the portion of the amplifying core other than the amplifying portion thereof and thus an amplifying ratio of the planar wave guide type optical amplifier as a whole cannot be also increased.